Parathyroid hormone in serum during lithium therapy.

In ten patients parathyroid hormone, urinary calcium excretion, and fractional tubular reabsorption of calcium were determined at intervals during three months of lithium treatment. Parathyroid hormone increased more than 40% within the first week and remained elevated throughout the treatment period. Calcium excretion fell by more than 30% within the first week and remained low throughout the treatment period. The reduction in urinary calcium excretion could be accounted for by an increase in fractional tubular reabsorption of calcium. There were no significant changes in serum calcium and inorganic phosphate or in urinary inorganic phosphate. The results indicate that lithium treatment affects the hormonal regulation of calcium metabolism.